Non-aqueous lithium electrochemical cells typically include an anode, an electrolyte comprising a lithium salt that is dissolved in one or more organic solvents and a cathode of an electrochemically active material, typically a chalcogenide of a transition metal.
Such cells, in an initial condition, are not charged. In order to be used to deliver electrochemical energy, such cells must be charged in order to transfer lithium to the anode from the lithium-containing cathode. During the initial charge, lithium ions are extracted from the cathode and transferred to the anode. During discharge, lithium ions from the anode pass through the liquid electrolyte to the electrochemically active cathode material of the cathode where the ions are taken up with the simultaneous release of electrical energy. During charging, the flow of ions is reversed so that lithium ions pass from the electrochemically active material through the electrolyte and are plated back onto the anode. Upon subsequent charge and discharge, the lithium ions (Li+) are transported between the electrodes. Such rechargeable batteries, having no free metallic species are called rechargeable ion batteries or rocking chair batteries. Rechargeable batteries and non-aqueous lithium electrochemical cells are discussed in U.S. Pat. Nos. 6,203,946; 5,871,866; 5,540,741; 5,460,904; 5,441,830; 5,418,090; 5,130,211; 4,464,447; and 4,194,062 the disclosures of which are incorporated herein by reference.
Sodium based active materials are described herein for use in ion batteries. The active materials may potentially offer some advantages, such as lower materials costs and the ability to utilize superior electrolyte systems. Until recently the problem with the practical realization of sodium ion batteries has been the lack of both anode (negative) and cathode (positive) electrode materials that could reversibly cycle sodium ions.